Effect of Biomass/Sludge Blending on the Emission Behavior of Heavy Metals during Coal Combustion: A Global Meta-analysis

Co-combustion of coal and carbon-containing fuels, especially biomass and sludge, is thought to be a good choice for the goal of carbon neutrality. Regardless of tremendous studies on the co-combustion characteristics, the effects of biomass/sludge blending on the emission behavior of toxic heavy metals are still not so clear due to the differences in volatility of heavy metals, the wide variety of raw blended materials, the changeable operating conditions, and the huge difference in experimental scale. To reach broad generalizations across larger numbers of study outcomes, a global meta-analysis was conducted in this work to comprehensively evaluate the impacts of various parameters on the emission of three typical heavy metals (As, Pb, and Cr). Results showed that co-firing with biomass/sludge would accelerate the emission of As and Pb while reducing Cr emission, mainly contributed by sludge rather than biomass. In comparison to other types of sludge, the promotion and inhibition effects of sewage sludge were more significant. The combustion temperature and blending ratio were the key factors affecting heavy metal emission, followed by the oxygen concentration and carbonization temperature of biomass. Besides, no remarkable difference was found among bench- and large-scale testing results. The findings are expected to give new insight into the clean co-combustion of coal and various kinds of solid wastes.